he could talk the dick off a wombat

Australian slang for someone who talks too much. Someone who keeps a conversation alive even after the other person has made cues to leave.

*someone talking to someone for 5 plus minutes, despite the opposite person trying to exit the building*
Person 1: "Strewth, old mate over there, he could talk the dick off a wombat with how long he's been chatting up this fella for".